Strongly overdoped states and irreversibility-field characteristics of the Hg-1223 and Cu-1223:P superconducting cuprates

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Abstract
Essentially single-phase Hg-1223 and Cu-1223:P samples in wide hole-doping ranges were successfully synthesized by a high-pressure (5 GPa) technique utilizing internal and/or external oxidizing agents and by subsequent post-annealings performed in a thermobalance. The hole-doping level of the as-synthesized samples was found to be in the overdoped side for both of the phases by thermoelectric power measurements. values as low as 107 K and 67 K were obtained for the overdoped Hg-1223 and Cu-1223:P samples, respectively. The values of and were calculated from the measured M versus H data employing, respectively, the Bean model and two different criteria: (at ) and (as ). It was found that the heavier the doped hole concentration was, the more improved were the versus characteristics for both the Hg-1223 and the Cu-1223:P phases. This tendency was the same for versus characteristics calculated using either criterion. The improvement with increasing hole-doping level was especially profound in the case of Cu-1223:P: the versus characteristics of a Cu-1223:P sample with K, probably being close to the optimally doped state, were as poor as that reported for Bi-2212, while an overdoped Cu-1223:P sample with K was superior to an overdoped Hg-1223 sample with K. The mechanisms as well as the usefulness of the observed phenomena are discussed.